There's a reason you've already forgotten your long weekend away

You can't just chill out on cue. SSaplaima / Shutterstock.com On the first day of a recent vacation, I found myself feeling, of all things, irritable.

I hadn't yet unpacked and couldn't find my hat. I was tired from the flight over, but couldn't get comfortable in the bed or on the couch. And worst of all, I was angry with myself for not having fun — this was a vacation, not a torture session, after all.

Over the next few days, I gradually slid into a "vacation routine," unpacked and unearthed the hat, and found the perfect napping position. Unfortunately, by the time I'd fully relaxed, our seven-day vacation was almost up. Time to readjust to reality!

A 2012 paper, published in the Journal of Happiness Studies, suggests I'm hardly the only person who needs a vacation adjustment period, even if they'd prefer not to.

According to the researchers, it takes eight days to completely let go. (The research was cited in a New York Times article by psychiatrist Richard Friedman.)

The researchers looked at 58 people — so the study was small — who were taking a vacation that lasted at least two weeks. They pinged people before and after the vacation, as well as several times during the vacation, and asked them to answer questions like, "How was your mood today?" and "How tense did you feel today?"

Results showed that health and well-being increased during the first four vacation days, and increased a lot between the fourth vacation day and the eighth, when it peaked.

The researchers cite other papers that suggest "it takes some time to wind down after a stressful work period and acclimatize to vacation."

It's probably similar to what happens when you get home after a long and stressful workday and can't fall asleep because your mind's still racing. As much as we'd like it to be, "on-cue relaxation" isn't a thing.

The greater takeaway here is that, if you can, plan a vacation that's at least eight days long. Otherwise you'll wind up in a situation where, by the time you get adjusted, it'll be time to leave.

That said, you don't need to plan a month-long getaway. As Business Insider's Chris Weller reported, a two-week vacation generally isn't more memorable than a one-week vacation. If you're planning a longer break, consider switching things up halfway through to maximize your happy memories.